Art of cracking hydrocarbons



Dec. 31, 1929. J. E. BELL ART OF CRACKING HYDROCARBONS Filed Jan. 22,1925 IIIL , n u l;

@SSX a im ATTORN EYS f /ZW/ L Patented Dec. 31, 1929 UNITED A STATESPATENT OFFICE JOHN E. BELL, DECEASECD, LATE F BROOKLYN, NEW YORK, BYLOLA R. BELL, EXECU- TRIX, OF BROOKLYN, NEW YORK, ASSIGNOR T0 SINCLAIRREFINING COMPANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE ART OFCRACKING HYDROCARBONS Application tiled January 22, 1925. Serial No.3,987.

operation of reflux or fractionating towersemplo ed in conjunction withpressure'cracking stills.

When heavy hydrocarbons are dlstllled under pressure, they are crackedwith the production of lighter oils. In the commercial operation of apressure still, some definite product or group of products, for examplegasoline or pressure' distillate, is usually desred but the vaporsescaping from the still itself may include heavier constituents inaddition to the constituents desired in the pressure distillate. Thevapors from the pressure still are commonl subjected to a refluxingoperation before veing condensed to effeet, to a greater or less extent,the return of such heavier vaporized constituents to the still forfurther'treatment therein,`- but, as ordinarily practised, such methodshave nevertheless resulted in the production of pressure distillatescontaining large amounts of constituents heavier than the desiredpressure distillate. For example, in treating gas oil for the productionof gasoline by such cracking methods, the pressure distillate usuallyincludes a considerable amount of constituents of a `kerosene characterand others even heavier, so that it is necessary to subject a relativelylarge amount of crude.

pressure distillate to redistillation to fractionate it intomerchantable products and to separate the heavier components.

It is'one of the objects of the present invention to eliminate suchredistillation of the pressure distillate as a separate operation and tosave heat usually employed for such redistillation. A Other and furtherobjects will appear more fully as the description proceeds.

According to the present invention, the heat of the pressure distillatevapors escaping from the pressure still is employed to -fractionate thepressure distillate in anim- 60 proved manner, .and it may also beemployed in an advantageous way for :tractionating at the same timeother oils or distillates including constituents suitable as componentsof lthe desired productor products.

According to the present invention, the vapors from the pressure stillare passed successively through two towers, charging stock to the stillis introducedv directly into the tower which the vapors first enter andreflux and admixed charging stock from this tower arev returned to thepressure still, and an oil or distillate including constituents suitableas components of the desired distillate is introduced directly into 'thesecond tower which the vapors escaping from the first enter.

In the first tower, the tower which the vapors rst enter, the vapors arecontacted with the charging stock introduced therein, the charging stockacting as a refluxing agent and refluxing the heavier constituents ofthe vapors to the still for further treatment in the still, while thecharging stock is at the same time preheated. The first tower-thus actsto effect an initial separation ofthe heavier cons'tituents and returnthem to the still and also to return to the still for useful applicationin the cracking operation therein a part of the heat of the escapingvapors. The vapors es`- caping from the first tower may comprise thenormal pressure distillate constituents, that is the components o f thedesired product associated with some heavier constituents but :freed ofthe heaviest constituents.

In the second tower, the tower which the vapors escaping from the firsttower enter, the vapors are contacted with an oil or distillateincluding constituents suitable as components of the desired distillatewhich constituents are thereby vaporized. The vapors entering the secondtower are partly cooled in the first tower and the vaporlzation ofcthelighter constituents of the oil introduced into the second tower furthercools them. The heavier constituents of the entering vapors are thuscondensed a d mix with the unvaporized constituents of the introducedoil, collecting as tower condensate. The vapors es-A caping from thesecond tower include the lighter constituents 'of the vapors enteringfrom the first tower and the light r constitmnL . densed in the usualWay. An accurate fractionation of the vapors from the still, and

likewise of the introduced oil, is thus eiected by the heat of thepressure distillate vapors, the condensate of the vapors escaping romthe second tower comprisingI the desired pressure distillatesubstantially free from heavier constituents, and the tower condensatecomprising the intermediate constituents heavier than the desiredpressure distillate components and lighter than the constituents reluXedto the pressure still from the first tower.

As compared to operations in which it is attempted to reflux directly tothe still from a reluXtower thereon (for example the first towerdescribed herein) all constituents heavier than lthe desired pressuredistillate, the process of the present invention accomplishes a markedheat economy. Where heavier constituents having a boiling point close tothe temperatures maintained in the pressure still.

are refluxed to the still theyv are cracked, with the production ofadditional amounts of the desired light constituents before they' arevaporized in the still; but wherev intermediate constituents, heavierthan desiredvrevaporizing in a cyclic manner these intermediateconstituentswithout cracking with a resulting decrease in therate ofcracking and the capacity of the pressure still.

In carrying out the present invention,

useless consumption of heat in revaporizing such intermediateconstituents is avoided while' the heat of the vapors is neverthelessemployed to advantage in fractionating the I vapors for the separationof apressure distillate of the desiredwcharacter. The heavierconstituents of the vapors, susceptible to furly ther cracking in thepressure still, are refluXed to the pressure still from the first tower,and the intermediate constituents heavier than suitable as components ofthe desired distillate are separated from the vapors in the secondtower. The condensate collecting in the second tower may be subjected tofurther cracking treatment, for example in a pressure still operated ata higher pressure or in vapor phase. cracking apparatus, or'it may bedisposed of otherwise;

The oil introduced into the second tower may be an oil or distillateindependent of the pressure still operation, or it may advantageously bea part of the final pressure distillate produced-in the operation rasthe condensatepf the vapors escaping from the second tower. Vhe're anindependent oil or distillate is employed it is in effect fractionallydistilled in the second towerby the heat of the vapors, the vaporized.constituents escaping with the uncondensed pressure distillate vaporsand the heavier unvaporized constituents collecting in admixture withthe pressure distillate vapor constituents condensed by the coolingeffect of the vaporization.

Where a part of the pressure distillate condensate is introduced, theintroduced oil is more or less completely vaporized, only the heaviestconstituents, 'if any,'remaining unvaporized, while the cooling effectof the vaporization ell'ects a sharp reluxing of the heavierconstituents of the pressure distillate vapors, particularly of theconstituents heavier than the vaporized constituents. A closefractionation between constituents suitable as components of the desiredpressure distillate and the heavier constituents is thus effected.-Where a part of the pressure distillate is so employed, the oilintroduced into the second tower contains no substantial amount ofconstituents heavier than the desired pressure distillate components andno heavier constituents can get into the pressure distillate from thatsource while the part of the pressure distillate returned is aneffective refluXing agent. In this way, by regulating the amount ofpressure distillate'introduced into the second tower, the character ofthe pressure distillate 9 as well as of the tower condensate can beclosely controlled.

The inventian will be further described in connection with theaccompanying drawings which show, in a 4somewhat diagrammatic andvconventional manner, an apparatus stapt-cd for the practice of theprocess of the rivention; but it is intended and will be understood thatthe invention is n'ot limited to the specific methods of operationdescribed in connection with this particular apparatus.

loll

The accompanying drawings represent, in Y V elevation and partly insection, a pressure still system adapted for the practice of theprocess" of the invention. The pressure cracking still illustrated inthe drawings is of the general construction and operation described andillustrated in United States Letters Patent No. 1,285,200 granted to the'Sinclair Refining Company, November 19, 1918 on the application ofEdward W. Isom. It will be apparent that theprocess of the invention maybe carried'out in connection with pressure` cracking stills of other anddifferent types.

llll

lll

The pressure still illustrated comprises the bulk supply tank 1 locatedaway. from the heating furnace, the vertically arranged heating tubes 2located in the heating ilue of the furnace, and circulating pipes 3, 4and 5 connecting successively the bulk supply tank, the

circulating pump 6, the lower end of the heating tubes, and the upperend-of the heating tubes and the bulk supply tank. A circulating pumpmay, with advantage, be employed for circulating the oil from the bulksupply tank through the heating tubes and back to the bulk supply tank;or the circulating pump may be omitted and thermosiphonic action reliedupon for maintaining circulation but with decreased still capacity.Arranged above the bulk supply tank is the re- Hux tower 7 having aseries of bailes therein and connected with the vapor dome of the bulksupply tank through the vapor line 8. 10 The pump 9 is arranged forintroducing fresh charging stock into the upper end of the reflux towerthrough connections 10 and 11; and the return reflux line 12 is arrangedfor returning reflux and admixed fresh oil from 15. the lower end of thereflux tower to the circulating connection 3 on the suction side of Pthe circulating pump. A connection 13 is also provided for introducingJfresh charging stock into the circulating oil through the bearings ofthe circulating pump. A connection 14 is arranged at the lower part ofthe circulating connect-ion for pumping out and charging the still, anda tar draw-off connection for use during the operation of the still isprovided at 15.

The second tower 16 is arranged beside the reflux tower 7 and a vaporconnection 17 is provided for conducting vapors from the upper end ofthe reflux tower to the lower of the second, or vfractionating, tower.The

vapors escape from the top of the second tower through the vapor line 18to the condenser 19 which is arranged to discharge into the receiver 20.From the receiver, the con- 5densed pressure distillate is dischargedthrough valved connection 21 and the uncondensed vapors and gasesthrough the valved connection 22. From the receiver, the condenseddistillate may be discharged into the pressure distillate tank 23, orthrough connection 24. ,The pump 25' is arranged for introducing arefluxing agent into the upper end of the fractionating tower throughconnecr tion 26. The refluxing agent so supplied may o be pressuredistillate withdrawn from the tank 23 withdrawn through vco-nnection 27or it may be supplied through a separate source from connection 28. Aconnection 30 is arranged for discharging the condensate mixtureproduced in the fractionating tower 16 from the lower end of thefractionating tower.

The pressure may be regulated and reduced by means of a regulating valve29 interposed between the fractionating tower and the condenser, or thestill pressure may be maintained through the condenser and the pressureregulated and controlled by a suitable eo valve or valves arrangedbeyond the condenser.

In carrying out the process of the invention in the apparatusillustrated, the pressure still is charged and brought to the crackingconditions of temperature and pressure in the usual way. As crackedvapors escape from the still additional charging stock is introducedthrough the reflux tower 7 and the charging stock and admixed relluxedconstituents are returned to the still from the reflux tower. Tai' maybe withdrawn as the operation proceeds, and the rate of tar withdrawaland the rate of supply of fresh charging stock may advantageously beregulated to maintain the concentration of pitch constituents in thecharge below saturation. The vapors escaping from the reflux tower 7enter the fractionating tower 16 where they are directly contacted withan oil refluxing agent introduced through connection 26. The suply ofrefluxing agent is regulated to control the character of the vaporsescaping from the fractionating tower and to condense in thefractionating tower the vapor constituents heavier than those suitableas components of the desired pressure distillate. The condensedconstituents of the yvapors and the unvaporized constituents of therefluxing agent are withdrawn through connection 30.

The vapors escaping from the fractionating tower are condensed in thecondenser 19 and the condensate collected as the desired pressuredistillate.

In cracking gas oil for the production of gasoline, for example, thestill is initially charged with gas oil and additional gas oil chargingstock is introduced through the reflux tower as the operation proceeds.The reflux returned to the still from the reflux tower includes any gasoil character constituents of the vapors and may also include heavierkerosene character constituents but 1S substantially free of gasolineconstituents. The vapors, including the gasoline constituents, escape tothe fractionating towerand a refluxing agent including gasolineconstituents is introduced into direct contact with the vapors in thefractionating tower.

introduced into the fractionating tower are vaporized by the heat of thevapors from the reflux tower and the vaporization of these constituentscools the vapors in the fraction ating tower. The supply ofrefluxmg'agent is regulated to absorb suflicient heat, 1n vaporizationof the lighter constituents thereof, to condense the vapor constituentsheavier than gasoline without `condensing the gasoline components. Theheavier constituents are thus condensed in the fractionating tower, andthe gasoline constituents of the cracked vapors together with thegasoline constituents of the reliuxing agent escape and are condensed asthe desired pressure distillate. A gasoline character pressuredistillate is thus produced directly.

For the production of gasoline, the refluxing agent may, for example, bea part of the pressure distillate, or a naphtha character fractionincluding gasoline constituents and The gasoline constituents of therefluxing agent heavier components such as kerosene constituents, or agasoline fraction such as a straight run gasoline to be blended with thepressure distillate may be employed as the reiuXing agent. Very closefractionation can be obtained by employing a part of the pressuredistillate itself, the reintroduced pressure distillatebeingsubstantially completely revaporized in the fractionatlng tower, theheat absorbed by the vaporization being available therein to effect thedesired fractional condensation. Where a naphtha character fraction isused, such as a crude pressure distillate as ordinarily produced inrunning for gasoline containin upwards of about 50% gasoline the napht aisl also fractionated in the fractionating tower, the heavierconstituents of the naphtha collecting with the condensate in the towerand the gasoline con' stituents escaping with the gasoline constituentsof the pressure still vapors. The operation of a pressure still inaccordance with the present invention may thus be combined withadvantage with other pressure still op ing the pressure distillate.

erations carried out in the usual manner, and the crude pressuredistillate from one or more other pressure stills fractionated, orredistilled, in conjunction with the pressure still operation of thepresent invention. The amount of crude pressure distillate which can beso fractionated will depend upon the relative proportion of gasolineconstituents in the crude pressure distillate as well as upon theconcentration of asoline constituents in the vapors entering t efractionating tower. A blending operation may also be advantageouslycombined with the process of the present invention and the gasoline, orgasoline fraction, for blending at, the same time utilized forfractionating the pressure dis-1 tillate vapors. In such a combinedblending operation, any heavier constituents of the asoline for blendingmay also be eliminated rom the composite pressure distillate. It willthus be seen that the present invention enables the direct production ofa pressure distillate substantially free from constituents heavier `thanthose suitableas components of the desired pressure distillate. The .v

elimination of such heavier constituents from the pressure distillate,or the increased concentration of the desired constituents in thepressure distillate, reduces the cost of refin- Redistillation may beavoided. The amount of pressure distillate that must be handled for eachgallon of the desired product is also reduced. This in turn reduces thelamount of equipment, labor and chemicals required for subsequentchemical treatment, and also reduces the amount of equipment, labor andfuel required if the pressure distillateis redistilled. The improvedfractionation effected 'also substantially eliminates from the pressuredistillate any entrained heavier constituents of the charging stockintroduced into theiirst tower on the still such as might carry withthem objectionable impurities or otherwise inter- The" improvedfractionation effected may also ac` fere with subsequentrefiningoperations.

all constituents heavier than desired as com-r y ponents of the pressuredistillate. The cooling of the pressure distillate vapors in the secondtower also assistsv in reducing the amount of cooling water employed forcondensing the pressure distillate.

Another important advantage of the present invention is that it does notrequire the use of bubble towers or other fractionating towers in whichthe iiow of vapors is materially restricted. One of the disadvantages ofsuch fractionating towers when employed in conjunction with pressurestills is the possibility of development of excessive pressures becauseof the restriction lof vapor -flow and, moreover, if the conditions inthe tower are disturbed a more or less prolonged period is required tobring the tower back to normal operation. In carrying out the presentinven-tion, on` the other hand, the second tower. maygibe of ordinarybaille construction prO- viding'a relatively large area for the freeiiow of the vapors. The path through such a tower is also relativelyshort and the heat exchanging relations in the tower are comparativelysimple and subject to' direct and immediate control. An'easil controlledand simple operation is thus provided while at the same time the directintroduction of part of the pressure distillate orof an oil containlngconstituent suitable as components of the pressure distillate" enablesclose fraction of the pressure, distillate and the substantialelimination otheavier consituents therefrom. Where an ordinary baiietowerl is so employed, a wide range of roducts can also be producedwithout ehangmg the design of the tower regulating the amount and'character of the reiuxing .medium introduced into the tower. y

It will also be-seen that the present invention provides an improvedmethod of frac` tionating pressure distillate, which in eiect may beconsidered a redistillation `of the pressure distillate in .which theheat of the pressure distillate vapors is em loyed in a particularlyadvantageous way gdr carrying out the redstillation. In the directproducf be improved, heavier constituents of the vapors escaping fromthe pressure stillsusceptible to further cracking treatment thereinbeing refluxed tothe still and part of the heat of the vapors beingreturned to the pressure still in thefresh charging stock for furtherapplication. to the cracking operation therein, and intermediateconstituents which might cause an excessive consumption of heat inrevaporization without useful cracking if returnedv directly to thestill charge being separated from the pressure distillate vapors withoutbeing returned to the pressure still.

What is claimed as new and desired to be secured byl Letters Patent ofthe United States is:

'1.An improved method of cracking gas oil for the production ofgasoline, which comprises heatmg a body of gas oil at the crackingtemperature by circulating oil from theV body through heating tubes andback to the body and distillng off vapors generated ation in directcontact with an oil including constituents suitable as components of thedesired pressure distillate, withdrawing an intermediate condensateincluding kerosene constituents from the fractionating operation wherebythe boiling range of the condensates returned to the distillng operationis restricted, condensing the vapors escaping from the fractionatingoperation, and supplying part wofthe condensate so produced to thefractionating operation as the oil including pressure distillateconstituents.

I aix my signature.

LOLA It. BELL,

Emea/,trim Qf tu'e Last Will ami Testamtefnt of JOLWE'. Bell, Deceased.

In testimony whereof thereby under pressure, subjecting the vapors fromthe distillng operation to a reluXing operationin direct contact withfresh gas oil charging stock, returning the reflux and admiXed gas oilconstituents lto the distillng operation, subjecting the vapors from thereluxing operation to a fractionating operation in direct contact withan oil containing gasoline constituents, withdrawing an intermediatecondensate including kerosene constituents from the fractionatingoperation whereby the boiling range of the condensatesreturned to thedistillng operation is restricted, withdrawing the gasoline constituentsfrom the fractionating operation as vapors and condensing them, andsupplying part of the condensate so produced to the fractionatingoperation as the oil containing gasoline constituents.

2. An improved method of cracking heavier hydrocarbon oils for theproduction thereby'under pressure, subjecting the vapors from thedistillng operation to a reiuxing operation, returning the reflux to thedistilling operation, subjecting the vapors from the reiluxingkoperationto a fractionating oper-

